1. Field of the Invention
The present invention relates to a powder-air separator for use in an apparatus for measuring out a predetermined quantity of powder into a vessel by first inhaling powder from a powder containing hopper into a powder quantity measuring chamber provided in the apparatus and then exhaling the powder from the chamber into a vessel to be charged with the powder.
2. Prior Art
In advance of describing prior art powder-air separators, a general constitution and performance of a powder filling apparatus in which powder-air separators are used is briefly described.
A typical powder filling apparatus which is used, for instance, in the pharmaceutical industry for measuring out a predetermined quantity of a powdered medicine into a vessel is illustrated in FIGS. 21 and 22. FIG. 21 shows the partially cut-out frontal view of the apparatus together with accompanying equipment, and FIG. 22 is the vertical cross-sectional view of the apparatus. According to the figures the apparatus comprises a vertically installed turret 11 provided with a plurality of powder quantity measuring chambers 13. Each of the chambers 13 is defined by a cylindrical hole 12 and a filter 1 attached on top of a filter carrier 2 inserted slidably in the hole 12. The filter carrier 2 has its tail 2a geared to a not shown mechanism for moving the same in the cylindrical hole 12 within a predetermined range. The volume of the chamber 13 can therefore be determined by a set position of the filter 1. The filter carrier 2 is made hollow under the filter 1, while the cylindrical hole 12 has its wall provided with an orifice 14 so that it may put in appearance at the hollow of the filter carrier 2. The orifice 14 is made to be selectively connected with a vacuum source 16 (FIG. 21) or a compressed air source 17 (FIG. 21) by means of a suitable air-vacuum switching means (not shown in the figures). On the upside of the turret 11, a hopper 18 (FIG. 21) which stores powder 19 is provided with its open bottom kept in contact with the circumference of the turret 11. In such an arrangement of the apparatus and related equipment, the turret 11 is intermittently rotated through a shaft 15 (FIG. 22) so that the powder quantity measuring chambers 13 may successively be brought under the hopper 18. Each time one powder quantity measuring chamber comes under the hopper 18, the orifice 14 related to that chamber is made to communicate with the vacuum source 16 to inhale the powder 19 into the chamber from the hopper 18. The chamber which once inhaled the powder remains connected to the vacuum source 16 through the orifice 14, lest the powder (should) be spilt out, until the chamber is brought, upside down, to the lowest position just above a vessel 20 (FIG. 21) waiting to be charged with the powder under the turret 11. With the opening of the chamber kept above the vessel, the orifice connection is switched to the compressed-air source 17 to exhale the powder into the vessel 20 in the form of a lump. In the above apparatus the filter 1 and the filter carrier 2 constitute a powder-air separator, which the present invention aims at improving.
In the following, some of the powder-air separators based on a prior art are shown in FIGS. 23, 24, 25 and 26, as being inserted in the above cylindrical hole 12.
The filter 1 of the powder-air separator shown in FIG. 23 is made up of bundled wires. This type of filter not only has its pore cross-sections distributed widely but also has its pores themselves made long and deep nearly along the directions of powder inhaling air streams, as indicated with arrows, so that smaller inhaled powder particles are liable to clog the filter, and what is unfavorable, in deep places. The clogging of the filter adversely affects both the powder inhaling and the powder exhaling performances of the powder-air separator.
In the other separators shown in FIGS. 24, 25 and 26, the filters 1 are all made by sintering substantially spherical metallic-particles, namely, made of an ordinary sintered metallic plate. The filters of this kind, however, have their porosity made relatively small, and therefore a higher pressure difference is needed for inhaling and exhaling powder. In addition, the pores made in the surface region are often bunt-shaped with their pore-openings made smaller than the inside cross-sections, as is schematically shown in FIG. 27, because the metallic particles 1b in the surface region are more strongly squeezed by a sintering pressure than those 1c located deep in the filter.
Accordingly, the powder particles once trapped in the surface pores are difficult to expel when the powder is exhaled. This causes the filter to be easily clogged. In FIG. 27, a reference number 19a shows trapped powder particles. Further, the conventional air-powder separators excluding the one which uses the filter shown in FIG. 23 have a dead space for sir streams on a marginal region of the filter, where the filter is attached to the filter carrier. The dead space, together with the clogging of the filter, causes detorioration of the performance of the separator, particularly the powder exhaling performance.